The present invention relates to the field of web splicing, and more particularly, to the field of web splicing equipment for joining the ends of sheet material such as paper.
The process of splicing a sheet (or xe2x80x9cwebxe2x80x9d) of material to another sheet of material is a common operation in a number of industries. In particular, in many paper industries, it is necessary to splice two webs of paper together in order to maintain a single unbroken web. This splicing operation is necessary for efficient operations downstream of the splicing equipment, which are fed with a steady and uninterrupted stream of web material. To maximize the efficiency of downstream operations, it is desirable to feed the web in a fast and steady manner without stopping or considerably changing the web speed. Conventional web splicing equipment is relatively inefficient, typically requiring the operator to stop the web or to significantly reduce web speed to splice the two ends of material.
In an effort to compensate for these inefficiencies, several conventional web splicing systems employ a variety of methods and assemblies to keep the web speed fed to downstream systems as fast and as continuous as possible. For example, as web material from an almost-expended roll (the xe2x80x9crunning rollxe2x80x9d) is fed at normal operating speed, certain systems will gradually bring a fresh roll of material (the xe2x80x9cready rollxe2x80x9d) up to the same speed, at which time the two webs are brought together and spliced. Such a system is disclosed in U.S. Pat. No. 3,252,671 issued to Phillips, Jr. et al. A drawback of such a system is that a large amount of web material which is fed through the splicer prior to the time the web speeds are matched is wasted during each splicing operation.
Other conventional web splicing systems perform their splicing operations by bringing the web from the ready roll up to speed very quickly. Such a system is disclosed in U.S. Pat. No. 5,252,170 issued to Schaupp. By bringing the ready roll web up to speed quickly, the material waste just described is avoided. However, systems which operate in this manner limit the types of web material which can be spliced. Many types of web material including, without limitation, toilet paper and tissue paper, are relatively low weight, low strength, and/or high stretch materials. Splicing operations performed by high-acceleration splicers on such materials perform poorly, and often result in ruptured webs or weak splices which are unable to withstand the rigors of downstream web operations.
Another disadvantage of many conventional web splicing systems (such as the one just described) is the manner in which the web splice is made. In particular, webs are often spliced by taping the ends of the two webs together. Especially in systems where the spliced area experiences a high amount of tension and/or in which the splicer does not provide a good speed match between the webs being spliced, a taped splice is often necessary. However, taped splices are undesirable because the spliced section of the web must eventually be removed from the web (for example, prior to the packaging of the final product) or the end products having the taped splice are must be discarded. Either method of discarding the tape spliced product section represents a waste of product. Furthermore, many tape splice systems require the operator to manually tape the two webs together. Not only does this typically require a section of both webs to be stationary for a period of time, but this is a labor-intensive inefficiency which is realized every time a splice is made.
As yet another example of how conventional web splicing systems attempt to feed downstream operations with a fast and continuous stream of web material through web splicing operations, certain systems use a bank of festoons or idler rolls immediately downstream of the splicer system. One such system is disclosed in U.S. Pat. No. 5,360,502 issued to Andersson. The festoon or idler rolls in such systems are adjusted to accommodate a significant amount of web material during normal web operations. When a web splicing operation is performed, the festoons or idler rolls move to release the web material wound therein. This process permits the web speed at the splice position (upstream of the festoons or idler rolls) to be temporarily reduced or stopped while the speed of the web material downstream of the festoons or idler rolls (i.e., for downstream machinery), is kept constant or only slightly reduced. When the splicing operation is complete, the web material passing the splicing area is brought back up to the speed of the web downstream of the festoons or idler rolls. A significant disadvantage of the web splicing system just described is the need for one or more banks of festoons or idler rolls and control elements and assemblies required for their operation. These components increase cost, maintenance, and floorspace requirements. Furthermore, it is of critical importance that a constant tension is maintained on the web throughout each operation performed upon the web. If constant tension is not maintained, web wrinkling and (in severe cases) web rupture can occur. Each festoon roll or idler roll added to a system creates web wrinkling and tensioning problems. Systems which attempt to address these problems by employing driven rolls in the bank of idler or festoon rolls inevitably introduce more expense, complexity, and maintenance costs into the system.
In view of the disadvantages of conventional web splicing systems noted above, there exists a need for a web splicing apparatus and method which can splice light weight, low strength, and high stretch web material without reducing the downstream speed of the web, which does not require additional elements or subsystems (e.g. a bank of festoon or idler rolls) to accommodate excess web material downstream of the splicer, and which can quickly and accurately accelerate a web up to the speed of a running web without the need for a taped splice and without the danger of web rupture during the splicing operation. The present invention provides such an apparatus and method.
An apparatus and method are provided for bonding one web of material (an xe2x80x9cinitially stationary webxe2x80x9d) to a moving web of material (an xe2x80x9cinitially moving webxe2x80x9d) without causing web rupture or web wrinkling. In order to quickly bring the initially stationary web up to the splicing speed without the need for slowing or stopping the initially moving web, the present invention employs a vacuum assembly which holds, pulls, and gradually accelerates the initially stationary web. The vacuum assembly preferably includes a first series of vacuum belts positioned to run around a series of pulleys. Within each vacuum belt is a at least one vacuum box. A vacuum is created within each vacuum box by a vacuum blower connected thereto. Each vacuum box preferably has an open face running behind a length of the corresponding vacuum belt""s path. A number of holes in a length of each vacuum belt preferably pass across the open face of the underlying vacuum boxes as the belts runs their paths, thereby temporarily creating suction through the holes which acts to hold web material to the first series of vacuum belts.
The tail of the initially stationary web is first placed over the vacuum belt holes, which are themselves initially positioned over the open faces of the vacuum boxes at their top ends. To ensure precise and controlled positioning of the vacuum belts (as well as to determine their speed), the vacuum belts are preferably toothed timing belts. The suction created through the holes by rile vacuum within the vacuum boxes holds the tail of the initially stationary web to the vacuum belts. When the splicing operation is begun, a belt motor turns the vacuum belts, which pulls the attached initially stationary web along a length of the vacuum belt path. The length over which the accelerating web is held allows for a gradual web acceleration and prevents web rupture.
A second series of vacuum belts and a corresponding second vacuum assembly preferably faces the first series of vacuum belts and corresponding first vacuum assembly. The second series of vacuum belts and corresponding second vacuum assembly is substantially the same in structure and operation as the first series of vacuum belts. To eliminate the need for web taping or web adhesive in the splicing operation, a pressure bonding mechanism is preferably located at the bottom portions of both the first and the second series of vacuum belts. Preferably, the pressure bonding mechanism is a series of ply-bond wheels attached for rotation at the bottom portions of the belts. Both series of vacuum belts and corresponding vacuum belt assemblies are preferably mounted to rotate about a top portion of the respective vacuum belts, thereby bringing the ply-bond wheels at the bottoms of both series of vacuum belts together. By the time the initially stationary web has been pulled by the first vacuum belts to the bottom of the path traveled by the belts, the bottoms of both series of vacuum belts have preferably been pushed or pulled together by one or more actuators. By this same time, the initially stationary web held to the first series of vacuum belts has reached the speed of the initially moving web, and can reliably be spliced to the initially moving web by passing both webs through the ply-bond wheels. As the holes holding the initially stationary web to the first series of vacuum belts reach the bottom of the path followed by the first series of vacuum belts, the holes pass from the open front face of the vacuum boxes, thereby releasing the initially stationary web to the adjacent ply-bond wheels. For more precise bonding, a primary actuator is preferably employed to move the bottoms of both series of vacuum belts and ply-bond wheels to a close position with respect to one another, while a series of fast secondary actuators are employed to push the ply-bond wheels together when the web sections to be spliced are reached. When the web sections to be spliced have passed through the ply-bond wheels, the secondary actuators and the primary actuator are retracted. Preferably at a time just prior to this, a cutting blade is actuated to sever the initially moving web near the top of the second series of vacuum belts. At this time, the holes within the second series of vacuum belts are located at the top of the second series of vacuum belts and hold the trailing end of the severed web as it proceeds down the second series of vacuum belts and between the ply-bond rolls.
To further assist the initially stationary web to come up to the speed of the initially moving web without rupturing, an idler roll immediately upstream of the first series of vacuum belts is preferably driven temporarily by a motor through a clutch. By driving the idler roll in this manner, the initially stationary web is not required to overcome the rotational inertia of the idler roll.
Typically, the two webs to be spliced are unwound from parent rolls which have high inertias. Therefore, the apparatus and method of the present invention preferably includes a dancer roll and substantially vertical dancer track located between each parent roll and the corresponding vacuum belts. Each dancer roll is preferably slidable within its associated dancer roll track, and has one of the two webs of material passed therearound. By moving the dancer roll up or down within the dancer roll track, the amount of material being passed to and from the dancer roll preferably increases and decreases, respectively. Dancer roll sensors are preferably used to detect the location of each dancer roll within its dancer roll track, and preferably provide this information to a controller which controls the rotational speed of the parent rolls. In this manner, excess web material can be accumulated by a dancer roll just prior to the acceleration of an initially stationary web and can be controllably released as the parent rolls driven up to splicing speed. This allows the end of the initially stationary web to quickly accelerate as described above while providing the slower parent roll enough time to come up to splicing speed. Similarly, at the end of the splicing process when one parent roll is decelerating, the dancer roll can be moved to take up the web unwinding during parent roll deceleration.